Styrene/anhydride polymeric material and graft having enhanced properties

ABSTRACT

A polymeric material from the styrene family comprises macromolecular chains grafted by nitrogen-containing heterocyclic groups; wherein the macromolecular chains comprise a polymeric backbone to which a grafted agent is attached by at least one covalent bond, the grafting agent comprises, in a single molecule, one or more associative groups capable of being bound by hydrogen bonds, and one or more reactive groups capable of forming covalent bonds with the polymeric backbone, at least one of the associative groups of the modifier is an imidazolidone heterocyclic ring. The mean number of imidazolidone groups to be inserted into the macromolecular chains is dependent both on the mean mass of said chains and on the final properties to be imparted to the material. Objects such as tubes, films, plates, stiffenerss, bottles and containers can be made.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.12/526,102, filed Nov. 24, 2009, which claims priority to InternationalApplication No. PCT/FRO8/050163, filed Feb. 1, 2008, and FrenchApplication FR 0753120, filed Feb. 7, 2007, the contents of whichapplications are incorporated by reference herein, in their entiretiesand for all purposes.

FIELD OF THE INVENTION

The present invention pertains to the field of styrenic polymerscomposed of macromolecular chains grafted with nitrogen-containingheterocycles and able to combine via hydrogen bonds. It also relates tothe compositions comprising such materials, and to their uses.

BACKGROUND OF THE INVENTION

Thermoplastics are useful in manufacturing articles in the sectors ofthe automotive industry and transport, the industry of electrical andelectronic appliances, including household electricals, the packagingindustry, such as that of microwavable food packaging, in theconstruction and decoration industry, in the mechanical industry and, ingeneral, in the industry of plastics, which relates to many and variedapplications such as in toys or office goods.

One of the most widely used classes of thermoplastics for theseapplications is that of rigid styrenic thermoplastics and, moreparticularly, that of rigid and transparent styrenic thermoplastics,such as polystyrene, which exhibits a number of advantages in this typeof application (optical and mechanical properties, low cost, ease ofuse, etc.), but which, unfortunately, does not exhibit very high heat orsolvent resistance.

The skilled person has therefore sought to copolymerize the styrene withother monomers, capable of providing the eventual copolymer with animprovement in its heat and solvent resistance, in relation tohomopolystyrene, while retaining good processability properties(capacity to be readily transformable). Accordingly patent US2971939describes a polymerization process producing copolymers of styrene andmaleic anhydride or blends of a styrene homopolymer with a copolymer ofstyrene and maleic anhydride, which have an improved heat distortiontemperature while retaining the processability of the material.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the stress-strain curves of an UDETA-grafted SMA and anungrafted SMA according to the mechanical 3-point flexural test.

DETAILED DESCRIPTION OF THE INVENTION

The applicant has now found a new polymer material exhibiting enhancedthermal properties (e.g. glass transition temperature) and/or enhancedsolvent resistance properties while retaining or likewise improving itsmechanical properties (e.g. mechanical moduli) and rheologicalproperties (e.g. the capillary viscosity or the low-shear viscosity)relative to the abovementioned prior-art polymer material.

The invention provides a graft copolymer obtained from the grafting:

-   -   of a copolymer (II) obtained from the copolymerization of at        least two monomers, (i) the first monomer being selected from        styrene and its derivatives and (ii) the second monomer        containing at least one anhydride function,    -   with molecules M-R-X (I) containing at least one unit (M)        selected from the units (1) to (4):

-   -   with A=oxygen, sulphur or NH;    -   and containing at least one chemical function (X) selected from        a halogen, a primary or secondary amine function, an alcohol        function, a thiol function, a carboxylic acid function or a        derivative of this function and an epoxy function, the unit (M)        and said function (X) being connected by a rigid or flexible        chain (R).

In one embodiment the graft copolymer is characterized in that thebackbone copolymer (II) for grafting is obtained from thecopolymerization of a mixture of monomers containing between 0.5% and50% (% by weight, relative to the total mixture of monomers) of monomercontaining an anhydride function.

In one embodiment the copolymer (II) is characterized in that themonomer containing an anhydride function is maleic anhydride.

In one embodiment the graft copolymer is characterized in that themolecules (I) are obtained from the reaction of urea with at least onecompound selected from alkyleneamines, amines, amino alcohols andamides.

In one embodiment the graft copolymer is characterized in that themolecules (I) are obtained from the reaction of urea with at least onecompound containing at least one primary amine function (—NH2) and atleast one secondary amine function (—NH—), said functions beingconnected by a carbon chain containing at least two carbon atoms.

In one embodiment the graft copolymer is characterized in that thefunction (X) is a primary or secondary amine function or an alcoholfunction.

In one embodiment the graft copolymer is characterized in that the unit(M) of the molecule (I) is the unit (1), which is an imidazolidoneheterocycle with A=oxygen.

In one embodiment the graft copolymer is characterized in that themolecule (I) is selected from the molecule UTETA, the molecule UTEPA andthe molecule UDETA.

In one embodiment the graft copolymer is characterized in that the chain(R) is a linear or branched alkyl chain composed of one to 30 carbonatoms, a ring or a succession of alkyl or aryl radicals joined bybridges —C(O)O—, OC(O), C(O), —O—, —S—, —NH— with, preferably, amolecular mass of R which is less than 1000 g/mol and very preferablyless than 500 g/mol.

In one embodiment the graft copolymer is characterized in that theaverage number of grafts is greater than 2 grafts per macromolecularchain.

The invention likewise provides a composition comprising a graftcopolymer as defined above and at least one other polymer.

The invention also relates to the use of the abovementioned graftcopolymer or of the composition set out above for manufacturing articlesintended for the sectors of vehicles, transport, electricity,electronics, information technology, medicine, packaging, includingmicrowavable food packaging, decoration, construction, mechanics, toysand/or household electricals. In one embodiment the invention relates tothe use of the graft copolymer:

-   -   as a compatibilizer in polymer blends    -   as a component of a polymer/additives masterbatch used for        additizing polymers which are identical to or different from the        graft copolymer.

The invention also relates to a process for synthesis of a graftcopolymer according to the invention, characterized in that it compriseseither (i) a step of dissolving molecules (I) and the copolymer (II) inan appropriate solvent, or (ii) a step of contacting the molecules (I)with the copolymer (II) in the melt state, without solvent, in anextruder, a calender or any other mixer.

The thermoplastic material of the invention is obtained by reacting:

-   -   molecules M-R-X (I) containing at least one unit (M) selected        from units (1) to (4) below and at least one function (X),        preferably selected from primary amine, secondary amine and        alcohol functions, and also a rigid or flexible spacer (R)    -   with a copolymer (II) obtained from the copolymerization of at        least two monomers, namely a styrenic monomer and a monomer        containing an anhydride function.

The copolymer (II) is obtained from the copolymerization of at least twodifferent monomers: a styrenic monomer, preferably styrene, and amonomer containing an anhydride function, preferably maleic anhydride.This copolymer (II) is abbreviated SMA. The copolymers SMA may also beobtained from copolymerizations with one or more other, further monomerssuch as, for example, acrylic comonomers such as alkyl(meth)acrylates.

The copolymer (II) is obtained from the copolymerization of a mixture ofmonomers comprising by weight, relative to the total mixture ofmonomers, between 0.5% and 50%, and preferably between 15% and 30%, ofmonomer containing an anhydride function.

At the time of the reaction of the copolymer (II) with the molecules(I), the anhydride functions of said copolymer (II) are opened by thefunction (X) of said molecules (I). The molecules (I) become grafted bycovalent bond(s) to the macromolecular chain of said copolymer (II).Although the stoichiometry of the reaction can be adjusted such thateach anhydride function of the copolymer (II) undergoes grafting, it ispreferable, especially when the proportion of anhydride functions in thecopolymer (II) exceeds 5% by weight, for the degree of grafting to theanhydride functions to be non-total; in other words, it is oftenpreferable for free anhydride functions to remain.

The structure of the graft copolymer is consequently modified on themolecular scale in that at least some of the macromolecular chains ofsaid copolymer contain grafts, comprising at least one of the units (1)to (4) below, said grafts being capable of combining with one another byreversible physical bonds such as hydrogen bonds. An average of morethan two grafts per chain of the copolymer (II) is needed for it to bepossible for a macromolecular network to be formed by virtue of hydrogenbonds. Without the explanation given limiting or confining in any waythe scope of the invention, the reversible physical interactions thattake place between grafts carried by different chains of the graftcopolymer, referred to as intermolecular physical interactions, arethought to make a decisive contribution to the improvement that isobserved in the properties of the graft copolymer relative to theproperties of the ungrafted copolymer.

The molecule M-R-X (I) comprises, united in a single molecule, at leastone unit (M) selected from units (1) to (4) below, said unit beingcapable of interacting by hydrogen bonding, and at least one function(X) which is capable of forming covalent bonds with the copolymer (II).The unit or units (M) and the function or functions (X) are joined toone another by a rigid or flexible chain (R).

The units (M) distinctively include the following:

with A=oxygen, sulphur or NH, advantageously oxygen.

The unit is preferably the unit (1) with A=oxygen, which is animidazolidone heterocycle.

The function (X) may be selected from a halogen, a primary or secondaryamine function, an alcohol or thiol function, a carboxylic acid functionor a derivative of these functions (ester, thioester, amide) and anepoxy function. Preferably (X) is a primary or secondary amine functionor an alcohol function.

The rigid or flexible chain (R) may be a hydrocarbon chain which carriesone or more heteroelements. It may be a linear or branched hydrocarbonchain composed of one to 30 carbon atoms, a ring or a succession ofalkyl or aryl elements joined by bridges —C(O)O—, OC(O), C(O), —O—, —S—,—NH—. The chain R according to the invention will have a molecular massof less than 1000 g/mol and preferably less than 500 g/mol.Advantageously, when these bridges are present in the chain (R), andespecially when they are amide bridges C(O)NH, they are capable ofcombining by hydrogen bonds.

If necessary, the grafting reaction of the molecule (I) to themacromolecular chain of the copolymer (II) will be able to producefurther groups which are associative by hydrogen bonding, and especiallyamide —C(O)NH— or —NHC(O)— bridges. Thus, when the unit X of themolecule (I) is an amine unit, the grafting reaction of the molecule (I)to the macromolecular chain of the copolymer (II) will be able to giverise to amide or imide bonds between the unit X and the carboxyl groupsof the anhydride units of the copolymer (II).

The molecules (I), comprising at least one unit selected from units (1)to (4) above, may be obtained from the reaction of urea with a moleculecontaining at least one primary amine function (‘3NH2) and at least onesecondary amine function (—NH—) which are separated by at least 2 carbonatoms, and more particularly are obtained from the reaction of urea withalkyleneamines, amines, amino alcohols or amides. The molecules (I) arepreferably selected from molecules (I) containing units (1) withA=oxygen, and are obtained from the reaction of urea with apolyalkylene-amine.

Mention may be made of the following:

-   -   the molecule UTETA:        1-(2-[(2-aminoethyl)amino]ethyl)imidazolidin-2-one, obtained        from the reaction of urea with triethylenetetramine (TETA);

-   -   the molecule UTEPA:        1-(2-{2-[(2-aminoethylamino]ethyl}amino)ethyl]-imidazolidin-2-one        obtained from the reaction of urea with tetraethylene-pentamine        (TEPA);

-   -   the molecule UDETA: 2-aminoethylimidazolidinone or        1-(2-aminoethyl)-imidazolidin-2-one, obtained from the reaction        of urea with diethylene- triamine (DETA);

-   -   and also molecules such as

obtained, for example, from the reaction of UDETA with, respectively, athio acid or a thio ester, a diacid or an acid ester and an amino acidor an amino ester.

The copolymer (II) is a copolymer obtained from the copolymerization ofat least 2 monomers, (i) the first monomer being selected from styreneand its derivatives in which at least one of the aliphatic or aromatichydrogens of the styrene is substituted, such as, for example,□-methylstyrene or 4-styrenesulphonate, and (ii) the second monomercontaining an anhydride function, such as, for example, maleicanhydride.

Preferably the copolymer is obtained by copolymerization of styrene andmaleic anhydride.

The reaction of the molecules (I) with the copolymer (II) may take placein solution or in the melt state. The molecules (I) and the copolymer(II) may be dissolved in an appropriate solvent, such as chloroform, byselecting the reaction temperature such that the reaction takes placewithin a reasonable time of from several minutes to several hours.Alternatively the molecules (I) may be contacted with the copolymer (II)in the melt state, without solvent, in such a way that this contact maytake place in thermoplastic polymer converting equipment that is wellknown to the skilled person, such as extruders, calenders and othermixers.

Generally speaking, the reaction of the molecules (I) with the copolymer(II) may take place by any process for chemical modification of polymersthat is known to a person skilled in the art, such as, for example,modification in solution, in which the reaction is performed in a commonsolvent for the polymer and for the reactants, followed by purificationby precipitation; or modification in the melt state, in which thereaction is performed by contacting the polymer and the reactants in themelt state in a suitable apparatus such as, for example, an internalmixer, or a continuous or batch co- kneader, or a single-screw or co- orcounter-rotating twin-screw extruder.

The nature of the intermolecular physical interactions produced by thegrafting carried out according to the invention means that theresistance of the polymer to the customary solvents is enhanced, whileleaving the possibility of redissolving the material in quite specificsolvents such as benzyl alcohol, whereas the improvement in the solventresistance by chemical crosslinking rules out any possible dissolution.

The graft copolymer according to the invention may be blended with atleast one other polymer to produce blends which are thermodynamicallycompatible, or to produce two-phase or multi-phase dispersions such asthose obtained when the thermoplastic SMA polymer is blended with apolymer capable of providing, in the eventual blend, the presence of anelastomeric phase which is capable of reinforcing the impact resistanceproperties of the material. Polymers capable of providing an elastomericphase in the blend include, as non-exclusive examples, polymers orcopolymers of butadiene or of isoprene, such as polybutadiene, such asSBR rubbers (styrene-butadiene rubbers), such as NBR rubbers(nitrile-butadiene rubbers), such as ABS(acrylonitrile-butadiene-styrene copolymers), such as MBS (methylmethacrylate-butadiene-styrene copolymers), such as block copolymers,for instance SBS (polystyrene-polybutadiene-polystyrene), SIS(polystyrene-polyisoprene-polystyrene) and SBM(polystyrene-polybutadiene-polymethyl methacrylate), and such ashydrogenated versions of these polymers and copolymers based onbutadiene or isoprene.

Mention may also be made of acrylic elastomeric polymers or copolymerssuch as the copolymers of styrene and butyl acrylate or the elastomericcopolymers based on polyolefins, such as ethylene-propylene copolymerelastomers, such as ethylene-propylene-diene copolymer elastomers, suchas polyisobutylene, such as modified ethylene-propylene copolymerelastomers and such as modified ethylene-propylene-diene (EPDM)copolymer elastomers.

The graft copolymer according to the invention may also be blended withat least one other polymer that does not contain an elastomeric phase,such as, for example, polystyrene, SAN (styrene-acrylonitrile copolymer)or SM (styrene-methyl methacrylate copolymer).

The polymer or polymers which may be blended with the graft polymer ofthe invention may optionally be themselves grafted with moleculescontaining grafts such as those of the invention or of chemicallydifferent type. Advantageously the use of polymers containing graftswhich are able to form hydrogen bonds with the grafts of the polymer ofthe invention is beneficial to the quality of the blend. The graftcopolymer of the invention is capable of blending more effectively withpigments, fillers or other additives that are commonly used in theplastics industry than is the ungrafted base copolymer. The copolymer ofthe invention advantageously may be used in masterbatches, which arepolymer/additive premixes containing a high concentration of additivesand which, by dilution in the polymer to be additized, will serve forbetter dispersing of said additives.

Lastly, the graft copolymer of the invention may also be used as acompatibilizer between two other polymers of a blend.

Description of a Working Example of the Invention EXAMPLE 1 ExtruderGrafting of an SMA Copolymer with UDETA

The SMA copolymer before grafting is an Aldrich product containing 14%by weight of maleic anhydride. Its number-average molecular mass, Mn, is85 000 g/mol and its weight-average molecular mass, Mw, is 188 000g/mol. Grafting is carried out in a DSM Micro 15 Compoundermicroextruder under a stream of nitrogen. The SMA is pretreated at 120°C. for 12 hours in an oven under vacuum, in order to reform theanhydrides, which are liable to undergo hydrolysis. 12 g of the SMA arethen mixed with 400 mg of UDETA with a molar purity of greater than 95%.The molecular mass of the UDETA molecule used to graft the SMA is 129g/mol. The extrusion temperature is 220° C. for screws which rotate at50 revolutions per minute. The material retains good processingproperties. The extruded product is subsequently introduced into a DACAInstruments injection-moulding machine, with an injection temperature of300° C. and a mould at 145° C. For comparison, the ungrafted SMAcopolymer is also injected at 300° C. with a mould at 140° C.

Mechanical 3-Point Flexural Test:

A mechanical test in three-point flexural mode is then carried out onbars in the shape of rectangular prisms, using a DMA TA 2980 instrument.An increasing-force ramp of 4N/min is applied and the mechanical modulusin flexure is thus determined. The UDETA-grafted SMA has a modulus of2.0 GPa, while the initial, ungrafted SMA has a modulus of 1.5 GPa,representing an increase of more than 33%. FIG. 1 shows thestress-strain curves of the UDETA-grafted SMA and ungrafted SMAaccording to this test. The greater slope of the plots of stress as afunction of strain for the grafted samples relative to the ungraftedsamples conveys the significant increase in the mechanical modulus.

Mechanical Tensile Test:

A tensile test is performed in an Instron 5564 tensile machine atambient temperature and with a pulling speed of 2 mm/min on dumbbellspecimens whose central portion measures 25 mm in length by 4 mm inwidth and 1.6 mm in thickness. This test demonstrates an increase in theYoung's modulus, which passes from 1.2 GPa for the ungrafted SMA to 1.4GPa for the grafted SMA, representing an improvement of more than 16%.

Solvent Resistance Test.

25 mg of ungrafted SMA are weighed out and introduced into a flaskcontaining 1 ml of chloroform. The same operation is repeated with 25 mgof grafted SMA in 1 ml of chloroform. The two solutions are subjected tostirring. After 8 hours, the grafted SMA has swollen but does notdissolve, whereas the ungrafted SMA dissolves rapidly. Identical resultsare found when the same experiment is reproduced using tetrahydrofuranin place of chloroform.40 mg of ungrafted SMA are weighed out and introduced into a flaskcontaining 2 ml of benzyl alcohol. The same operation is repeated with40 mg of grafted SMA in 2 ml of benzyl alcohol. The two solutions areheated at 125° C. and subjected to stirring. After 1 day, the graftedSMA has dissolved, making the solution turbid, and the ungrafted SMA hasdissolved completely.

Thermal Analysis:

Samples of grafted SMA and ungrafted SMA each of 10 mg are analysed bycalorimetry using a DSC TA Q1000 instrument operating in T4 mode. Theglass transition temperatures of these two materials are estimated withheating and cooling rates of 10° C./min. The grafted SMA has a glasstransition temperature that is 5.4° C. higher than the ungrafted SMA(135.5° C. and 130.1° C. respectively).

EXAMPLE 2 Extruder Grafting of an SMA Copolymer with a Smaller Amount ofUDETA

The SMA copolymer before grafting is the same as that of Example 1.Grafting is carried out in a DSM Micro 15 Compounder microextruder undera stream of nitrogen. The SMA is pretreated at 120° C. for 12 hours inan oven under vacuum, in order to reform the anhydrides, which areliable to undergo hydrolysis. 12 g of the SMA are then mixed with 170 mgof UDETA with a molar purity of greater than 95%. The extrusiontemperature is 220° C. for screws which rotate at 50 revolutions perminute. The material retains good processing properties. The extrudedproduct is subsequently introduced into a DACA Instrumentsinjection-moulding machine, with an injection temperature of 300° C. andwith a mould at 140° C.

Mechanical 3-Point Flexural Test:

A mechanical test in three-point flexural mode is then carried out onbars in the shape of rectangular prisms, using a DMA TA 2980 instrument.An increasing-force ramp of 4N/min is applied and the mechanical modulusin flexure is thus determined. The grafted SMA has a modulus of 1.84GPa, while the initial SMA has a modulus of 1.5 GPa, representing anincrease of more than 22%.

Solvent Resistance Test:

25 mg of ungrafted SMA are weighed out and introduced into a flaskcontaining 1 ml of chloroform. The same operation is repeated with 25 mgof grafted SMA in 1 ml of chloroform. The two solutions are subjected tostirring. The grafted SMA dissolves, but makes the solution very hazy,whereas the solution with the ungrafted SMA is completely transparent.Identical results are found when the same experiment is reproduced usingtetrahydrofuran.40 mg of ungrafted SMA are weighed out and introduced into a flaskcontaining 2 ml of benzyl alcohol. The same operation is repeated with40 mg of grafted SMA in 2 ml of benzyl alcohol. The two solutions areheated at 125° C. and subjected to stirring. After 1 day, the graftedSMA has dissolved, making the solution very slightly hazy, and theungrafted SMA has dissolved completely.

Thermal Analysis:

Samples of grafted SMA and ungrafted SMA each of 10 mg are analysed bycalorimetry using a DSC TA Q1000 instrument operating in T4 mode. Theglass transition temperatures of these two materials are estimated withheating and cooling rates of 10° C./min. The grafted SMA has a glasstransition temperature of 2.7° C. higher than the ungrafted SMA (132.7°C. and 130.1° C. respectively).

The graft copolymer according to the invention, in pure form,constitutes a new, rigid and transparent thermoplastic material. Thegraft copolymer according to the invention, integrated in a composition,constitutes a new, transparent, translucent or opaque thermoplasticmaterial. The graft copolymer of the invention, in pure form or as partof a composition, constitutes a thermoplastic material which, afterapplication steps which are well known to the skilled person (such asextrusion, injection moulding, thermoforming or calendering), allows themanufacture of plastics articles. Said articles may have applications inall of the fields in which plastics are used, such as the field of motorvehicles, transport, electricity, electronics, information technology,medicine, packaging, including microwavable food packaging, decoration,construction, mechanical engineering, toys and household electricals.The graft copolymer according to the invention may also play a part as:

-   -   a compatibilizer in a composition comprising among other        components at least two polymers belonging to different polymer        classes    -   a component of a masterbatch with a high concentration of        additives (such as pigments or fillers) for additizing polymers        or copolymers which are identical or different from that of the        invention.

EXAMPLE 3 Twin-Screw Extruder Grafting of a Commercial Grade of SMA withUDETA

The SMA copolymer before grafting is a Xiran, produced by Polyscope,containing 22% by weight of maleic anhydride. Its weight-averagemolecular mass, Mw, is 110 000 g/mol. The grafting of UDETA onto SMA iscarried out in a process of reactive extrusion on a Leistritz LSM30-34twin-screw extruder, with a diameter of 34 mm and a length-to-diameterratio of 30. The temperature profile is regulated at 200° C. flat, theflow rate at 20 kg/h and the rotary speed of the screws at 300revolutions per minute. The SMA is introduced in a hopper, and UDETA isinjected in zone 2 by means of a membrane metering micropump(Prominent); the flow rate is monitored by loss of weight on a balance.A degassing zone allows for removal of any volatile compounds. TheUDETA, with a purity of more than 80% by weight, is introduced at 1.5%by mass, relative to the SMA-UDETA combination. At the exit of theextruder, the product is cooled and pelletized. The SMA is also extrudedon its own.

Infra-red Analysis

Samples of grafted and ungrafted SMA are analysed by infra-redspectroscopy by germanium crystal ATR. The spectrometer is a protected460 ESP from Nicolet; the ATR cell is a Thunderdome from Spectra-tech.The absorption band of the anhydride, which is situated at 1775 cm⁻¹, isreduced after grafting, while a band appears at around 1705 cm⁻¹, whichshows that grafting has indeed taken place.

Rheological Analysis

Tests in a capillary rheometer and a rotational rheometer are performedon samples of grafted and ungrafted SMA (both extruded), both of whichhave been stored in an oven at 150° C. under vacuum overnight in orderto remove any trapped gases. These measurements are performed at 230° C.

Capillary rheometer: a Gottfert Rheotester capillary rheometer with adie possessing a length-to-diameter ratio of 30 is used. A Rabinowitschcorrection is applied for all of the tests. The viscosity values 1 arepresented in Table 1 below:

TABLE 1 Viscosity at 11 s⁻¹ Ungrafted SMA 1483 Pa · s Grafted SMA 2425Pa · s

An increase is observed in the low-shear viscosity after grafting.

Rotational rheometer: a Physica MCR 301 rotational rheometer equippedwith parallel plates with a diameter of 25 mm is used in frequency sweepmode. The deformation applied varies between 2% and 6%, so as to remainin the linear range. The moduli of the complex viscosities measured attwo frequencies are presented in Table 2 below:

TABLE 2 Complex viscosity at 0.628 rad/s Complex viscosity at 135 rad/sUngrafted SMA 1900 591 Grafted SMA 3040 610

The viscosities are virtually identical at high frequencies, but that ofthe grafted SMA is very much higher than that of the ungrafted SMA atlow frequencies. The ease of shaping of these products (high shearrate), also referred to as “processability”, will be little affected,since it is governed by the high-shear viscosity, whereas operationsinvolving low shear rates (such as the melt strength) will be greatlymodified by the grafting; in other words, the grafted SMA will flow lessunder its own weight.

EXAMPLE 4 Twin-Screw Extruder Grafting of a Commercial Grade of SMA withTwo Different Proportions of UDETA

The SMA copolymer before grafting is a Xiran SZ26080, produced byPolyscope, containing 26% by weight of maleic anhydride. Itsweight-average molecular mass, Mw, is 80 000 g/mol. The grafting ofUDETA onto SMA is carried out in a process of reactive extrusion on aLeistritz LSM30-34 twin-screw extruder, with a diameter of 34 mm and alength-to-diameter ratio of 30. The temperature profile is regulated at200° C. flat, the flow rate at 20 kg/h and the rotary speed of thescrews at 300 revolutions per minute. The SMA is introduced in a hopper,and UDETA is injected in zone 2 by means of a membrane meteringmicropump (Prominent); the flow rate is monitored by loss of weight on abalance. A degassing zone allows for removal of any volatile compounds.The UDETA, with a purity of more than 80% by weight, is introduced at1.5% and 3% by mass. At the exit of the extruder, the product is cooledand pelletized.

Infra-Red Analysis

Samples of grafted and ungrafted SMA are analysed by infra-redspectroscopy by germanium crystal ATR. The spectrometer is a protected460 ESP from Nicolet; the ATR cell is a Thunderdome from Spectra-tech.The greater the level of grafting, the more the extent to which theabsorption band of the anhydride, which is situated at 1775 cm⁻¹, isreduced, and the more the band at around 1705 cm⁻¹ increases, showingthat grafting has indeed taken place.

Thermal Analysis

Samples of grafted SMA and ungrafted SMA (both extruded) are analysed bycalorimetry using a Netzsch DSC 204F1 instrument. The glass transitiontemperatures of these two materials are estimated with heating andcooling rates of 20° C./min. The glass transition temperature ismeasured on the second heating. The ungrafted SMA has a glass transitiontemperature of 156° C., in comparison to 158.1° C. for the grafted SMAwith 1.5% of UDETA, and 158.7° C. for the grafted SMA with 3% of UDETA.

Rheological Analysis

Tests in a capillary rheometer are carried out on grafted and ungraftedSMA samples, both treated overnight in an oven at 150° C. under vacuumin order to remove any trapped gases. These measurements are made at230° C. A Gottfert Rheotester capillary rheometer with a die possessinga length-to-diameter ratio of 30 is used. A Rabinowitsch correction isapplied for all of the tests. The following viscosity values areobtained:

TABLE 3 Viscosity at 12 s⁻¹ Grafted SMA with 1.5% of 2920 Pa · s UDETAGrafted SMA with 3% of 3870 Pa · s UDETA

An increase in the degree of grafting produces an increase in thelow-shear viscosity. Operations involving low shear rates (such as meltstrength) will be greatly modified by the grafting; the greater theextent to which the SMA is grafted with UDETA, the less it will flowunder its own weight.

EXAMPLE 5 Twin-Screw Extruder Grafting of a more Fluid Commercial Gradeof SMA with Two Different Proportions of UDETA

The SMA copolymer before grafting is a Xiran SZ22065, produced byPolyscope, containing 22% by weight of maleic anhydride. Itsweight-average molecular mass, Mw, is 65 000 g/mol. The grafting ofUDETA onto SMA is carried out in a process of reactive extrusion on aLeistritz LSM30-34 twin-screw extruder, with a diameter of 34 mm and alength-to-diameter ratio of 30. The temperature profile is regulated at200° C. flat, the flow rate at 20 kg/h and the rotary speed of thescrews at 300 revolutions per minute. The SMA is introduced in a hopper,and UDETA is injected in zone 2 by means of a membrane meteringmicropump (Prominent); the flow rate is monitored by loss of weight on abalance. A degassing zone allows for removal of any volatile compounds.The UDETA, with a purity of more than 80% by weight, is introduced at1.5% and 3% by mass. At the exit of the extruder, the product is cooledand pelletized. The SMA is also extruded on its own.

Infra-Red Analysis

Samples of grafted and ungrafted SMA are analysed by infra-redspectroscopy by germanium crystal ATR. The spectrometer is a protected460 ESP from Nicolet; the ATR cell is a Thunderdome from Spectra-tech.The greater the level of grafting, the more the extent to which theabsorption band of the anhydride, which is situated at 1775 cm⁻¹, isreduced, and the more the band at around 1705 cm⁻¹ increases, showingthat grafting has indeed taken place.

Thermal Analysis

Samples of grafted SMA and ungrafted SMA (all extruded) are analysed bycalorimetry using a Netzsch DSC 204F1 instrument. The glass transitiontemperatures of these two materials are estimated with heating andcooling rates of 20° C./min. The glass transition temperature ismeasured on the second heating. The ungrafted SMA has a glass transitiontemperature of 149.1° C., in comparison to 152.4° C. for the grafted SMAwith 1.5% of UDETA, and 153.7° C. for the grafted SMA with 3% of UDETA.

Rheological Analysis

Tests in a capillary rheometer are carried out on grafted SMA samplesand on the two ungrafted SMAs containing different proportions of UDETA,both being treated overnight in an oven at 150° C. under vacuum in orderto remove any trapped gases. These measurements are made at 230° C. AGottfert Rheotester capillary rheometer with a die possessing alength-to-diameter ratio of 30 is used. A Rabinowitsch correction isapplied for all of the tests. The following viscosity values areobtained:

TABLE 4 Viscosity at 11 s⁻¹ Viscosity at 1000 s⁻¹ Ungrafted SMA  810 Pa· s 215 Pa · s Grafted SMA with 1.5% of 1710 Pa · s 260 Pa · s UDETAGrafted SMA with 3% of 2360 Pa · s 330 Pa · s UDETA

An increase in the degree of grafting produces an increase in viscosity,particularly in the low-shear viscosity. Operations involving low shearrates (such as melt strength) will be greatly modified by the grafting;the greater the extent to which the

SMA is grafted with UDETA, the less it will flow under its own weight,whereas the conditions of use will be affected to less of an extent,since it is the high-shear viscosity which controls the flow inapplication.

1. A process for synthesis of a graft copolymer obtained by grafting: acopolymer (II) obtained from the copolymerization of at least twomonomers, (i) the first monomer being selected from styrene and itsderivatives and (ii) the second monomer containing at least oneanhydride function, with molecules M-R-X (I) containing at least oneheterocycle unit (M) selected from the group consisting of units (1) to(4):

with A=oxygen, sulphur or NH; and containing at least one chemicalfunction (X) selected from a halogen, a primary or secondary aminefunction, an alcohol function, a thiol function, a carboxylic acidfunction or a derivative of this function and an epoxy function, theunit (M) and said function (X) being connected by a rigid or flexiblechain (R), wherein the molecules (I) are obtained from the reaction ofurea with at least one compound containing at least one primary aminefunction (—NH₂) and at least one secondary amine function (—NH—), saidfunctions being connected by a carbon chain containing at least twocarbon atoms.
 2. A process according to claim 1, wherein the copolymer(II) is obtained from the copolymerization of a mixture of monomerscontaining by weight, relative to the total mixture of monomers, between0.5% and 50% of monomer containing an anhydride function.
 3. A processaccording to claim 1, wherein the monomer containing an anhydridefunction is maleic anhydride.
 4. A process according to claim 1, whereinthe molecules (I) are obtained from the reaction of urea with at leastone compound selected from alkylene amines, amines, amino alcohols andamides.
 5. A process according to claim 1, wherein the function (X) is aprimary or secondary amine function or an alcohol function.
 6. A processaccording to claim 1, wherein the unit (M) of the molecule (I) is theunit (1), which is an imidazolidone heterocycle with A=oxygen.
 7. Aprocess according to claim 6, wherein the molecule (I) is selected fromthe molecule 1-(2-[(2-aminoethyl)amino]ethyl)imidazolidin-2-one (UTETA),the molecule1-[(2-{2-[(2-aminoethyl)amino]ethyl}amino)ethyl]imidazolidin-2-one(UTEPA), and the molecule 2-aminoethylimidazolidinone or1-(2-aminoethyl)imidazolidin-2-one (UDETA).
 8. A process according toclaim 1, wherein the chain (R) is a linear or branched alkyl chaincomposed of one to 30 carbon atoms, a ring or a succession of alkyl oraryl radicals joined by bridges —C(O)O—, OC(O, C(O), —O—, —S—, —NH—. 9.A process according to claim 8, wherein the chain (R) has a molecularmass of less than 1000 g/mol.
 10. A process according to claim 1,wherein the average number of grafts is greater than 2 grafts permacromolecular chain.
 11. A process according to claim 2, wherein thecopolymer (II) is obtained from the copolymerization of a mixture ofmonomers containing by weight, relative to the total mixture ofmonomers, between 15% and 30%, of monomer containing an anhydridefunction.
 12. A process according to claim 10 wherein the chain (R) hasa molecular mass of less than 500 g/mol.
 13. A graft copolymercomprising: a copolymer (II) grafted with molecules M-R-X (I) comprisinga nitrogen-containing heterocyclic group, the copolymer (II) obtainedfrom the copolymerization of a first monomer comprising styrene orderivatives thereof and a second monomer comprising at least oneanhydride function, the molecules M-R-X (I) comprising anitrogen-containing heterocyclic group (M) selected from the groupconsisting of units (1) to (4):

where A=oxygen, R is a hydrocarbon chain, and X is selected from ahalogen, a primary or secondary amine function, an alcohol function, athiol function, a carboxylic acid function or a derivative of thisfunction and an epoxy function, and the graft copolymer comprises morethan two grafts per chain of the copolymer
 14. The graft copolymer ofclaim 13, wherein the unit (M) of the molecule (I) is the unit (1). 15.The graft copolymer of claim 14, wherein the molecule (I) is selectedfrom the molecule 1-(2-[(2-aminoethyl)amino]ethyl)imidazolidin-2-one(UTETA), the molecule1-[(2-{2-[(2-aminoethyl)amino]ethyl]amino)ethyl]imidazolidin-2-one(UTEPA), and the molecule 2-aminoethylimidazolidinone or1-(2-aminoethyl)imidazolidin-2-one (UDETA).
 16. The graft copolymer ofclaim 13, wherein the function (X) is a primary or secondary aminefunction.
 17. The graft copolymer of claim 13, wherein the chain (R) isa linear or branched alkyl chain composed of one to 30 carbon atoms. 18.The graft copolymer of claim 13, wherein the chain (R) has a molecularmass of less than 1000 g/mol.